This invention relates to a coin detecting device in a coin sorting machine used, for instance, in an automatic vending machine, in which a sorting coil for inspecting the characteristics of a coin inserted thereinto is arranged along a coin rolling passageway, and the variation in impedance of the sorting coil caused when a coin passes through the sorting coil is detected to determine whether the coin is a true coin or a false coin. Such a coin detecting device positively discriminates coins different in monetary value from one another but equal in physical characteristics to one another and detects the passage of each coin inserted thereinto.
Typically, the following three coin sorting systems employing the sorting coil described above are known in the art. A first one is a bridge circuit system in which a bridge circuit is constituted by the sorting coil, a standard impedance element compared with the sorting coil, and two fixed elements, and the balance of the bridge circuit which takes place when a coin passes through the sorting coil is detected. A second one is a frequency detection system in which an oscillation circuit is made up of the sorting coil employed as its oscillation element, and the variation of the oscillation frequency of the oscillation circuit which takes place when a coin passes through the sorting coil is detected. A third one is an induced voltage detecting system in which the sorting coil is constituted by a signal transmitting coil and a signal receiving coil which are arranged on both sides of a coin passageway, and the variation of a voltage induced in the signal receiving coil when a coin passes between the two coils is detected. These systems are similar to one another in that a coin is sorted out depending on whether or not a sorting signal based on the output of the sorting coil adapted to detect the material, thickness, diameter, shape, etc. of a coin is within a predetermined coin determination reference range.
In sorting out coins according to the bridge circuit system, the bridge circuit is balanced by inserting a true coin, and the output of the bridge circuit is zero. However, when a false coin which is equal in material to a true coin but larger in diameter that the true coin is inserted, the impedance variation of the sorting coil is greater than that in the case of inserting the true coin, and therefore the bridge circuit is balanced twice. In other words, the amount of impedance variation of the sorting coil with the false coin is greater than the amount of impedance variation of the sorting coil with the true coin, and therefore the point where the impedance of the sorting coil coincides with the impedance of the sorting coil which satisfies the balance condition of the bridge circuit occurs twice. Thus, the bridge circuit twice provides the output which is similar to that provided when the true coin is inserted, which results in an error. Such an error takes place also in the frequency detection system and the induced voltage detecting system.
In a coin sorting machine for sorting out coins in various monetary denominations, it is necessary to sort out coins separately according to the denominations and to distribute them separately according to the denominations. However, if coins different in denomination are successively inserted into the machine and the distance between adjacent coins rolling along the coin passageway is less than a predetermined value, before the condition of a coin distributing member is changed from its condition for the first coin to its condition for the second coin, the second coin reaches the coin distributing member, as a result of which the second coin is distributed in the same manner as the first coin. Therefore, in the case where the inserted coins are to be put into, for instance, a coin tube where coins used as change money are to be stacked, coins different in denomination may be put in the same coin tube. In addition, if the diameter of the second coin is larger than the diameter of the first coin, coin jamming may be caused in the machine.
In order to overcome the above-described difficulty, there has been proposed a coin sorting machine in which first and second coin detecting switches are provided respectively upstream and downstream of a sorting coin along the coin passageway, the first coin detecting switch spaced a predetermined distance from the second one, to thereby detect the position of a coin rolling along the coin passage. In this conventional machine, the period of time which elapses from the instant that an inserted coin is detected by the first coin detecting switch until the inserted coin is detected by the second coin detecting switch is employed as a coin sorting period, and when a coin sorting signal is provided only once during the coin sorting period, the coin is determined as a true coin, and when the coin sorting signal is provided twice or more or no coin sorting signal is provided, the coin is determined as a false coin. Furthermore, in the same machine, in order to detect the fact that the distance between adjacent coins inserted thereinto is less than the predetermined value, it is detected if, during the period of time which elapses from the instant that the firstly inserted coin is detected by the first coin detecting switch until it is detected by the second coin detecting switch, the secondly inserted coin is detected by the first coin detecting switch. In other words, if, before the firstly inserted coin is detected by the second coin detecting switch, the secondly inserted coin is detected by the first coin detector, then the coin insertion is determined as successive coin insertion.
With this machine, it is possible to segregate a false coin which is equal in material to a true coin but larger in diameter than the true coin, from the true coin, and to detect the successive coin insertion with ease. Since coins to be sorted out by the machine are current coins, some of them are worn out. In general, such worn-out coins are abraded at their peripheral portions. Accordingly, in order to determine the worn-out coin as a true coin, the balance state of the bridge circuit is detected with a certain tolerance such that it is determined as a true coin not when the bridge output is completely zero but when the bridge output approaches zero. Therefore, the conventional machine has a high probability of accepting an unwanted coin which is different in denomination from a wanted coin which is to be sorted out but similar in characteristic to the wanted coin. In other words, the unwanted coin equal in material and thickness to the wanted coin but different in diameter and configuration from the wanted coin is segregated as acceptable together with the wanted coin. More specifically, a German 1-mark coin and a British 5-pence coin are segregated as the same denomination coins.
In a particular coin sorting system, a false coin different in material and thickness from a wanted coin to be sorted out may sometimes be sorted out as a true coin. In general, such false coins are different in configuration, outside diameter and appearance (coin surfaces). The detailed description of kinds of coins to be sorted out, and kinds of coins or false coins (hereinafter referred to as particular coins, when applicable) similar in characteristic to the coins to be sorted out, will be omitted, as to do otherwise may cause a social problem. At any rate, it is necessary to provide an apparatus which is capable of rejecting particular coins and coins which may be newly publicly issued by the government and are similar in characteristic to the existing coins, without greatly modifying the conventional coin sorting machines, and which apparatus can be utilized for sorting out the particular coins.